Cancer has an identical meaning with malignant tumor and indicates a state where regulation of cellular growth is damaged due to various causes and thus abnormal cells excessively grow and thus invade surrounding tissues and organs, form masses, and destroy normal tissues. Cancers typically exhibit rapid growth, invasiveness (penetrate into or spread out), and metastasis (moves to the remote place), which eventually leads to a life-threatening condition.
Liver cancer is one of the most lethal cancers worldwide, and the death toll from liver cancer each year exceeds half million people in Asia and Sub-Saharan Africa. Liver cancer is classified into primary liver cancer (hepatocellular carcinoma) that originates from liver cells and metastatic liver cancer that originates from other malignant tissues. More than 90% of the liver cancer is primary liver cancer, and therefore, liver cancer is typically understood as indicating primary liver cancer.
Although the etiological agents of hepatocellular carcinoma are well known to be an acute or a chronic hepatitis with hepatitis B virus and hepatitis C virus infection, the molecular mechanism in vivo of hepatocarcinogenesis has not been clarified.
Previous studies identified that cancers including liver cancer are induced by mutation of proto-oncogenes such as growth factors to oncogenes which leads to overexpression and overactivation of oncogenes, or by mutation of tumor suppressors such as RB and p53 which leads to their loss of function or underexpression. Especially, the relevance of genes such as mutated p53, beta-catenin, axin 1, p21(WAF1/CIP1), and p27Kip, etc to hepatocellular carcinoma has been identified. However, the current view on cancers have changed such that it is now understood that cancers including liver cancer are not caused by a few genes alone, but originated from the complex interactions of many genes related to cell cycle and signal transduction processes. Therefore, rather than focusing on expression levels and functions of a few genes or proteins, a more comprehensive analysis of diverse set of genes and proteins would be required.
Cancer is known to be the most typical refractory disease. Treatments of cancers can be categorized as surgery, cancer chemotherapy, and radiation therapy. Other treatment methods include locoregional therapy, hormone therapy, photodynamic therapy (PDT), laser therapy etc, and more recently immunotherapy and gene therapy is attempted. For a successful treatment of cancer, the early detection of cancer is essential.
More than 90% of early stage cancers can be treated completely with less than 5% recurrence rate. However, cancers, especially liver cancer, do not show any observable symptoms that enables early detection of cancer, thus there is a difficulty in detecting a cancer early by a conventional method.
Several methods are under development for early detection of cancer, one of which is utilizing cancer specific markers that are originated from bodily fluids and tissues that indicates in the presence of cancer. Genes or proteins that are specifically overexpressed or underexpressed in cancer cells can be used as cancer specific markers. The presence of these cancer specific markers in the tissues or bodily fluids from the patients at risk of cancer can be used to diagnose cancer. For example, AFP is known as a liver cancer marker, which is present at very low levels in normal adults (less than 7-10 ng/mL), but at much higher levels in 50-70% of HCC patients. These cancer specific markers can provide possibility of early detection of cancer due to their easy and accurate diagnostic utility, provide clues to the mechanism of carcinogenesis through in-depth study of their functions, and ultimately provide staring points for development of cancer treatment and prevention. Thus, development of cancer specific markers has important meanings for both academic and medical aspects.
Previous research on liver cancer markers include Xu et al. [Xu et al., Cancer Res. 61:3176-3181, 2001] that described analysis of cDNA library from 29 liver cancer tissues and matching surrounding normal tissues and found genes frequently expressed in hepatocellular carcinoma: serum albumin, α1-antitrypsin, inter-alpha-trypsin inhibitor, Apolipoprotein AII, fibrinogen, selenoprotein P, aldolase; Park et al. [Park et al., Int. J. Cancer 62:276-282, 1995] that reported increased expression of transferrin, IGF-II (insulin-likegrowth factor II), IGF-1R (insulin growth factor-1 receptor), and Fas-ligand related to apoptosis in HCC.
Previous patent documents on liver cancer markers are Korean patent No. 552,494 (registered in 2006 Feb. 8) that described liver cancer specific overexpression of K-ALPHA-1 (NM—006082), LDHA (NM—005566), FTL (NM—000146), ANXA2 (NM—004039), RPL4 (NM—000968), ENO1 (NM—001428), RPL9 (NM—000661), GNB2L1 (NM—006098), RPL10 (NM—006013), RPL13A (NM—012423) and liver cancer specific underexpression of AMBP (NM—001633), SERPINC1 (NM—000488), GC (NM—000583), A1BG (NM—130786) genes; Korean patent No. 777088 (registered in 2007 Nov. 9) that described LCN2 (NM—005564), MIDKINE (NM—002391, NM—001012333, NM—001012334), TFPI (NM—006287); Korean patent No. 2007-99312 (2007 Oct. 9) that described HLA-DMA (NM—006120), CD24 (NM—013230), SDFR1 (NM—012428); Korean patent No. 767,878 (registered in 2007 Oct. 10) that described UBD (Hs.44532), PRKAG1 (Hs.3136), CSTB (Hs.695), PSORS1C1 (Hs.507), TUBBS (Hs.110837), Hs.62914, UBPH (Hs.3459), SPARC (Hs.111779), PDHB (Hs.161357), EIF4B (Hs.93379), ABCB10 (Hs.1710), NDFIP2 (Hs.30340), SPAG7 (Hs.90436), RAN (Hs.10842), DDIT4 (Hs.111244), RPS20 (Hs.8102), C9orf9 (Hs.62595), TBC1D14 (Hs.72242), PIP5K2A (Hs.108966), SNX22 (Hs.157607), C9 (Hs.1290), CYP2E1 (Hs.75183), ZFP36L1 (Hs.85155), C6 (Hs.1282), BHMT (Hs.80756), MICAL3 (Hs.165551), DKFZp434C0328 (Hs.24583), GZMB (Hs.1051), PCK1 (Hs.1872), UGT2B7 (Hs.10319), MGC45564 (Hs.132230), UBE4A (Hs.75275), KIAA0316 (Hs.92025), ADH1C (Hs.2523), RPS9 (Hs.139876), SFXN1 (Hs.135742), SLC12A8 (Hs.36793), APOA1 (Hs.93194), BF (Hs.69771), and ACAT1 (Hs.37). However, the liver cancer markers listed in the above patent documents have been identified at the DNA or mRNA level rather than at the proteome level, and none of them used early HCC tissues. The genetic material in cancer cells are typically unstable such that the expression levels of genes unrelated to cancer are often affected, and thus, the applicability or clinical accuracy of liver cancer markers identified at the DNA or mRNA level using fully-developed cancer tissues are questionable. Therefore, there is still a need for clinically applicable and accurate liver cancer markers.
Proteome is the whole gamut of proteins that can be synthesized from genome, which is a dynamic entity that reflects changes within specific physiological and pathological states of cells or tissues. Proteomics is the area of research that encompasses the methods and techniques to characterize proteome, focusing on characteristics of proteins in relation with gene expression, post-translational modification, protein complex formation to comprehensively understand changes and network formation within cells and progression of diseases. Thus, Proteome represents the physiological and pathological states within cells and tissues, and thus it is one of the best approaches to find diagnostic markers of diseases. Further, if the expression of certain genes induces carcinogenesis, the protein coded by such genes could be identified and used as target proteins for drug development. The development of diagnostic and therapeutic drugs are under way using genomics approach because of its high sensitivity and easy amplification of genetic materials. However, the changes at the DNA or mRNA level may not lead to changes at the protein level, undermining the usefulness of markers developed at the DNA or mRNA level. Furthermore, in case of genetic materials that cannot be easily acquired for bodily fluids, proteomics analysis is the most practical approach. The body fluids such as plasma, serum, urine, cerebrospinal fluid, amniotic fluid, and secreting fluid are used for non-invasive approaches towards diagnosis of the disease and many researchers rely on proteomics methods to develop specific protein markers.